frexp, frexpf, frexpl
| Defined in header <math.h>
|
||
| float frexpf( float arg, int* exp ); |
(1) | (since C99) |
| double frexp( double arg, int* exp ); |
(2) | |
| long double frexpl( long double arg, int* exp ); |
(3) | (since C99) |
| Defined in header <tgmath.h>
|
||
| #define frexp( arg, exp ) |
(4) | (since C99) |
x into a normalized fraction and an integral power of two.arg has type long double, frexpl is called. Otherwise, if arg has integer type or the type double, frexp is called. Otherwise, frexpf is called, respectively.Parameters
| arg | - | floating point value |
| exp | - | pointer to integer value to store the exponent to |
Return value
If arg is zero, returns zero and stores zero in *exp.
Otherwise (if arg is not zero), if no errors occur, returns the value x in the range (-1;-0.5], [0.5; 1) and stores an integer value in *exp such that x×2(*exp)
=arg.
If the value to be stored in *exp is outside the range of int, the behavior is unspecified.
If arg is not a floating-point number, the behavior is unspecified.
Error handling
This function is not subject to any errors specified in math_errhandling.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
- If
argis ±0, it is returned, unmodified, and0is stored in *exp. - If
argis ±∞, it is returned, and an unspecified value is stored in *exp. - If
argis NaN, NaN is returned, and an unspecified value is stored in *exp. - No floating-point exceptions are raised.
- If FLT_RADIX is 2 (or a power of 2), the returned value is exact, the current rounding mode is ignored
Notes
On a binary system (where FLT_RADIX is 2), frexp may be implemented as
The function frexp, together with its dual, ldexp, can be used to manipulate the representation of a floating-point number without direct bit manipulations.
Example
#include <stdio.h> #include <math.h> #include <float.h> int main(void) { double f = 123.45; printf("Given the number %.2f or %a in hex,\n", f, f); double f3; double f2 = modf(f, &f3); printf("modf() makes %.0f + %.2f\n", f3, f2); int i; f2 = frexp(f, &i); printf("frexp() makes %f * 2^%d\n", f2, i); i = ilogb(f); printf("logb()/ilogb() make %f * %d^%d\n", f/scalbn(1.0, i), FLT_RADIX, i); }
Possible output:
Given the number 123.45 or 0x1.edccccccccccdp+6 in hex, modf() makes 123 + 0.45 frexp() makes 0.964453 * 2^7 logb()/ilogb() make 1.92891 * 2^6
References
- C11 standard (ISO/IEC 9899:2011):
- 7.12.6.4 The frexp functions (p: 243)
- 7.25 Type-generic math <tgmath.h> (p: 373-375)
- F.10.3.4 The frexp functions (p: 521)
- C99 standard (ISO/IEC 9899:1999):
- 7.12.6.4 The frexp functions (p: 224)
- 7.22 Type-generic math <tgmath.h> (p: 335-337)
- F.9.3.4 The frexp functions (p: 458)
- C89/C90 standard (ISO/IEC 9899:1990):
- 4.5.4.2 The frexp function
See also
| (C99)(C99) |
multiplies a number by 2 raised to a power (function) |
| (C99)(C99)(C99) |
extracts exponent of the given number (function) |
| (C99)(C99)(C99) |
extracts exponent of the given number (function) |
| (C99)(C99) |
breaks a number into integer and fractional parts (function) |
| C++ documentation for frexp
| |